The present invention relates to an image processing apparatus and an image processing method for storing image data and attribute data obtained by extracting a feature of the image data, and an image forming apparatus having the image processing apparatus.
In recent years, along with an increase in speed or the amount of information, as represented by the Internet, a digital multifunction product installed in an office has functions, such as a document filing process in which created documents, drawings, etc., are merged into a database and filed, in addition to processes such as facsimile, print, and copying. Thus, the digital multifunction product is shared by many users and has begun to process a large amount of image data at high speed.
Conventionally, a digital multifunction product has a fast accessible semiconductor memory as a primary storage device (image memory) and a hard disk drive (HDD) with a relatively low access speed as a secondary storage device. Image data obtained by reading a document is compressed and the compressed image data is stored on the HDD while being buffered in the primary storage device, whereby a large amount of image data is processed as fast as possible and the storage capacity of the entire storage device is reduced. Alternatively, image data obtained by reading a document is compressed and the compressed image data is stored on the HDD. Then, the compressed image data is read from the HDD where necessary, data for image formation is generated based on the read compressed image data, and the generated data for image formation is subjected to image formation (printing process) while being buffered in the primary storage device, whereby a large amount of image data is processed as fast as possible and the storage capacity of the entire storage device is reduced.
As an example of a reduction in storage capacity, Japanese Patent Application Laid-Open No. 11-239321 proposes a digital camera in which a compression process by JPEG format is performed on camera data and compressed image data is overwritten so as to avoid a camera data area that is not subjected to the compression process, whereby the storage capacity is reduced.
In a digital multifunction product, to implement reproduction of high image quality for a variety of documents, in addition to image data, a feature (e.g., concentration information or a concentration gradient of an area around an observed pixel which is obtained by a local mask) of the image data is extracted. Then, based on a result of the extraction, attribute data (e.g., characters or a photo) to be used for determination of a document type and a necessary process is generated. The image data is different from the attribute data and their compression methods are also different from each other.
Thus, when image data and attribute data are compressed and buffered in a primary storage device (image memory), different storage areas need to be provided for the image data and the attribute data, respectively. For example, FIGS. 1A and 1B each are a schematic diagram showing an exemplary memory map of a conventional image memory (primary storage device). FIG. 1A shows a memory area d1 for compressed image data and a memory area a1 for compressed attribute data which are used to buffer (store) compressed image data and compressed attribute data before the compressed image data and the compressed attribute data are stored on a secondary storage device (e.g., an HDD), the compressed image data and the compressed attribute data being obtained by compressing image data obtained by reading a document (A4, color) of a single page, for example, and attribute data generated based on the image data. The memory area d1 for compressed image data and the memory area a1 for compressed attribute data are contiguously provided.
When there are a plurality of pages of documents, memory areas for compressed image data and memory areas for compressed attribute data d2, a2, d3, a3, . . . (none of which is shown) are further contiguously provided for storing compressed image data and compressed attribute data corresponding to image data units obtained from a document of the second page, a document of the third page, . . . , respectively. The memory sizes of the memory area d1 for compressed image data and the memory area a1 for compressed attribute data are set by determining in advance the compression ratios of respective image data and attribute data. FIG. 1B shows an image memory occupancy status when compressed image data and compressed attribute data are written.
When compressed image data and compressed attribute data are decompressed and data for image formation is generated based on the decompressed image data and the decompressed attribute data and then buffered in a primary storage device (image memory), different storage areas need to be provided for the decompressed image data and the decompressed attribute data, respectively.
For example, FIG. 2 is a schematic diagram showing another exemplary memory map of a conventional image memory (primary storage device). For example, image data obtained by reading a document (A4, color) of a single page and its attribute data are compressed and the compressed image data and the compressed attribute data are stored on a secondary storage device (e.g., an HDD). When an image is formed based on the image data stored on the HDD, the image data and the attribute data stored on the HDD are stored (buffered) in an image memory. In this case, as shown in FIG. 2, a memory area that stores the compressed image data and a memory area that stores the compressed attribute data are contiguously provided.
The compressed image data and the compressed attribute data which are stored in the image memory are read, the read compressed image data and compressed attribute data are decompressed, and data for image formation (YMCK data) is generated based on image data and attribute data obtained by the decompression. The data for image formation is written in a memory area that is different from the memory areas where the compressed image data and the compressed attribute data are stored, whereby buffering of the data for image formation is performed.